This invention relates to an improved, organic solvent based, wood preservative composition which provides improved stability, which includes a combination of a fungicide, including a boron-containing compound, at least one triazole compound, and an organo iodine compound, an insecticide, including a synthetic pyrethroid, and optionally water repellants and/or other organic insecticides, and which provides resistance to insect attack on wood treated with this combination.
Wood and wood-based materials, including cellulosic composites and plastic-wood composites, are susceptible to damage from insect pests including ants, beetles and termites. The Formosan subterranean termite, Coptotermes formosanus Shiraki, is of particular concern since this termite species is the most widely distributed and damaging termite pest in tropical and subtropical regions of the world. It is responsible for tens of millions of dollars each year in costs of damages and control in the State of Hawaii, and it is an increasingly serious problem across the southern United States. The rapid feeding rate, large colony size and aggressive foraging of this termite species make it especially challenging with respect to effective wood treatment substances for protecting wood and wood products from attack by this particular pest.
A variety of fungicides including or combined with boron compounds have been used to protect wood and wood composites from decay. For example, it is known to use zinc borate to protect cellulosic composites, including particleboard, hardboard and oriented strand board, from fungal decay, as described in U.S. Pat. Nos. 4,879,083; 5,763,338; and 5,972,266. Zinc borate is usually applied as a powder or a liquid suspension to wood chips or strands, prior to their fabrication into panels. However, zinc borate is not a very cost-effective wood preservative, and does not provide good protection against mold, mildew and staining fungi at typical use levels.
Boric acid forms white, needlelike crystals in which the B(OH)3 units are linked together by hydrogen bonds to form layers of nearly hexagonal symmetry. The boric acid crystals are not very soluble, and in fact, the solubility of boric acid in cold water is only about 63.5 grams/liter at room temperature. So, saturated aqueous solutions of boric acid can contain no more than about one percent-by-weight boron. Liquid boron solutions have been prepared by dissolving an inorganic borate, e.g., sodium borate, in water. Because the borates are not significantly more soluble than boric acid, the maximum concentration of boron which can be achieved with saturated borate solutions is only about three percent-by-weight. See, for example, the Handbook of Chemistry and Physics, 54th Edition, CRC Press, Cleveland, Ohio, pages B-74 and B-136.
Other attempts to increase the concentration of boron in solution have involved the reaction of boron compounds, e.g., boric acid and the borates, with polyamines and alkanolamines to produce polyborates. Because these polyborates are more soluble in water, aqueous solutions containing higher boron concentrations may be prepared.
Other examples of boron containing compositions have been suggested for use as wood preservatives include U.S. Pat. No. 4,911,988 which teaches the use of boro-organic ester compounds to make shaped elements that are inserted into the preformed cavities in timber or other materials. U.S. Pat. No. 6,416,789 teaches a synergistic combination of fungicides, including boron-containing compounds, organo-iodine compounds, and amine-oxides. U.S. Pat. No. 5,846,305 discloses a wood preservative composition comprising a copper compound, an amine solvent and a boron compound. U.S. Pat. No. 6,582,732 teaches a synergistic combination of insecticides including boron-containing compounds and synthetic pyrethroids. Also, a wood preservers are sold by Blackfriar, as a combination of trihexyleneglycol biborate (THGB) and naphta, for red cedar, by Triton as a paste combination of THGB and permethrin, by Palace as a combination of THGB and cypermethrin. These compositions are simple, two component, solvent based, preservative compositions and do not contain other or multiple organic fungicides, water repellants, or other compositions.
It is also known to use iodopropargyl derivatives such as 3-iodo-2-propynyl-n-butyl carbamate (IPBC) for protection against fungi which cause structural and cosmetic damage to wood. However, while effective, this compound used alone is expensive and requires larger amounts to achieve the desired end result. U.S. Pat. No. 5,389,300 provides a composition for protecting sawn timber against wood discoloring fungi, containing a phenol fungicide and an organo-iodine fungicide such as IPBC. Other fungicides, insecticides, or active ingredients, including boron compounds, can be added to the composition.
U.S. Pat. No. Re 36,798 provides a preservative composition for treatment of wood and other cellulosic materials, comprising a biocidal metal compound and a fungicidal compound containing a triazole group. Compositions of this invention may contain other organic fungicides, insecticides, or bacteriocides, including boron in any form, such as boric acid, boron, or boron esters. U.S. Pat. No. 4,950,685 relates to a wood preservative composition which provides stain resistance to wood. The composition comprises a synergistic combination of a quaternary ammonium compound and IPBC.
U.S. Pat. No. 5,990,043 relates to an anti-fouling composition which includes a carrier, a binder, and an effective amount of at least one insecticide, which can be a carbamate. Synergistic effects are observed when combinations of two or more of the numerous insecticides listed are used in combination.
A variety of insecticides, including creosote, chrome-copper-arsenate, organophosphates and boron compounds, are available to protect wood and wood composites against insect attack. Synthetic pyrethroids are also used to protect against pests but are not as economical or easy to use in the amounts needed for sufficient pest control. For example, U.S. Pat. Nos. 5,480,638 and 5,575,996 disclose a powdered insecticide bait composition comprised of pet food, powdered pyrethrin and boric acid. U.S. Pat. No. 5,516,620 relates to a controlled release composition in which a insecticide is encapsulated in a starch-borax-urea matrix. U.S. Pat. No. 5,880,142 discloses a composition suitable for controlling termites comprised of a compound of a specific chemical formula used in combination with a pyrethroid. U.S. Pat. No. 5,916,356 discloses a wood preservative composition comprising a synergistic combination of a biocidal metal compound and a fungicidal compound having a triazole group. The biocidal metal compound can be zinc in the form of an inorganic salt such as zinc borate.
The problem with combinations of preservatives, especially when combined in organic and waterborne solvents, is that they can be unpredictably unstable or have limited stability such that they must be used quickly once mixed or they have no or little “shelf life”. As noted in U.S. Pat. No. 5,151,127 which teaches a composition containing a fire retardant and wood preservation compounds, including boron and boron oxide compounds, “the component compounds of the compositions are mixed in specific sequences to avoid coagulation of the mixture.”